环形桁架结构模态实验及有限元仿真分析

Modal experiment analysis and FEM simulation for a ring truss structure

针对大型可展开环形桁架天线结构开展了模态实验和有限元仿真分析。首先设计加工了环形桁架实验模型,采用锤击法对自由边界条件下环形桁架结构进行了实验模态分析,得到环形桁架结构的前六阶固有频率及其对应模态振型,并通过模态置信准则对实验结果进行了可靠性分析。其次,建立了环形桁架实验模型的有限元模型并进行模态分析,仿真得到其前六阶固有频率和模态振型。最后详细对比分析了实验结果与有限元仿真结果。结果表明:二者固有频率误差小于5%,且实验模态振型与有限元仿真模态振型一致,证明了本文分析结果真实可靠;同时,分析得到了环形桁架结构第一、二阶振型为椭圆形,第三、四阶振型为三角形,第五、六阶振型为四边形。

In this paper, the modal experiment analysis and FEM（finite element method） simulation of a ring truss structure which modeled a large deployable antenna are carried out. First, an experimental model for the large deployable antenna astromesh is designed and manufactured. And the experimental modal analysis of the ring truss under the free boundary condition is conducted by using hammer method. Based on the experiment results, the first six order natural frequencies, and the first six order mode shapes are obtained. And the MAC（Modal Assurance Criterion） is introduced to verify this experimental results. Secondly, modal analysis of the ring truss structure under the free boundary condition is conducted by using FEM. The first six order natural frequencies and corresponding damping ratio and the first six order mode shapes are also obtained. Finally, the results between the experiment method and FEM are compared. It is found that the error for the natural frequencies is acceptable while the mode shapes show very good agreement. In summary, the results of the different methods have good consistency, which can confirms that the analysis of this paper is feasible and reliable. Meanwhile, the natural frequency and mode shape of each order are obtained.